Injection apparatus

ABSTRACT

An object is to reduce the axial dimension of an injection apparatus ( 31 ), facilitate the work of removing and inserting a screw ( 20 ), and improve the quality of molded products. The injection apparatus ( 31 ) comprises a heating cylinder ( 17 ), a screw ( 20 ), and a drive apparatus. The screw ( 20 ) includes a plasticizing portion which includes a body portion ( 45   a ) and a flight ( 53 ) projectingly formed on an outer circumferential surface of the body portion ( 45   a ). An index ε, which is obtained by dividing a value obtained by adding a screw stroke S and a screw effective length L together by the screw stroke S, satisfies the relation 2.0&lt;ε&lt;4.5. Even when the screw ( 20 ) is shortened, resin can be melted satisfactorily. Accordingly, the axial dimension of the injection apparatus ( 31 ) can be reduced.

TECHNICAL FIELD

The present invention relates to an injection apparatus.

BACKGROUND ART

Conventionally, in a molding machine; for example, in aninjection-molding machine, resin heated and melted in a heating cylinderis injected under high pressure and charged into a cavity of a moldapparatus, and the injected resin is cooled and solidified in thecavity, whereby a molded product is obtained.

For such a molding operation, the injection-molding machine includes amold apparatus, a mold-clamping apparatus and an injection apparatus.The mold-clamping apparatus includes a stationary platen and a movableplaten. The movable platen is advanced and retreated by means of amold-clamping cylinder, whereby the mold apparatus is closed, clamped,and opened.

Meanwhile, the injection apparatus, which is generally of an in-linescrew type, includes a heating cylinder for heating and melting resinfed from a hopper, and an injection nozzle for injecting the moltenresin. A screw is disposed in the heating cylinder in a reciprocativeand rotatable condition. When the screw is advanced by means of a driveapparatus connected to the rear end thereof, resin is injected from theinjection nozzle. When the screw is retreated by means of the driveapparatus, metering of resin is performed.

FIG. 1 is a cross sectional view showing a main portion of aconventional injection apparatus. FIG. 2 is a schematic view showing astate where resin is melted within the conventional injection apparatus.FIG. 3 is a view used for explaining a developed distance of theconventional injection apparatus.

In FIG. 1, reference numeral 11 denotes a heating cylinder. An injectionnozzle 12 is attached to the front end of the heating cylinder 11, andheaters h1 to h3 for heating the heating cylinder 11 are disposed aroundthe heating cylinder 11. A screw 14 is disposed within the heatingcylinder 11 such that the screw 14 can rotate and can advance andretreat. The screw 14 is composed of a flight forming portion 15 and aninjection portion 16, and is connected to an unillustrated driveapparatus via a shaft portion 21 at the rear end and a coupler 22. Theinjection portion 16 is composed of a head portion 41, a rod portion 42extending rearward from the head portion 41, a check ring 43 disposedaround the rod portion 42, and a seal ring 44 attached to the front endof the flight forming portion 15. Notably, the head portion 41, the rodportion 42, etc. constitute a screw head. Further, the check ring 43 andthe seal ring 44 serve as a reverse-flow prevention apparatus forpreventing reverse flow of resin during an injection step. The driveapparatus is composed of an injection motor and a metering motor. Theflight forming portion 15 includes a bar-shaped body portion and aspiral flight 23 formed on the outer circumferential surface of the bodyportion, so that a spiral groove 24 is formed along the flight 23.

A resin supply port 25 is formed in the heating cylinder 11 in thevicinity of the rear end thereof, and a funnel-shaped hopper 26 isdisposed at the resin supply port 25. Resin in the form of pelletsstored in the hopper 26 is supplied to the interior of the heatingcylinder 11 via the resin supply port 25.

The resin supply port 25 is formed at a location such that the resinsupply port 25 faces a rear end portion of the groove 24 when the screw14 is positioned at the fowardmost position within the heating cylinder11; i.e., at the advance limit position. The flight forming portion 15has a supply portion P1, a compression portion P2, and a meteringportion P3, formed in this sequence from the rear end to the front end.The supply portion P1 receives the resin supplied via the resin supplyport 25. The compression portion P2 melts the supplied resin whilecompressing the resin. The metering portion P3 meters a predeterminedamount of the molten resin each time.

In the injection apparatus having the above-described configuration, ina metering step, the screw 14 is rotated through drive of the meteringmotor. Thus, the resin supplied from the hopper 26 into the heatingcylinder 11 is caused to advance along the groove 24 to thereby passthrough the supply portion P1, the compression portion P2, and themetering portion P3 successively, and is heated by the heaters h1 to h3during the advancement. Further, the resin receives a shear force in aspace (shearing space) formed between the inner circumferential surfaceof the heating cylinder 11 and the groove 24, so that the resingenerates heat (hereinafter referred to as “shearing heat generation”),and melts. With this operation, the screw 14 is retreated.

Since the check ring 43 moves forward in relation to the rod portion 42as the screw 14 is retreated, the resin having reached the front end ofthe flight forming portion 15 passes through a resin passage between therod portion 42 and the check ring 43, and reaches a space locatedforward of the screw head. Accordingly, an amount of molten resincorresponding to a single shot is accumulated forward of the screw head,in a state in which the screw 14 is positioned at the rearwardmostposition within the heating cylinder 11; i.e., at the retreat limitposition.

Subsequently, in an injection step, the screw 14 is advanced throughdrive of the injection motor, whereby the resin accumulated forward ofthe screw head is injected from the injection nozzle 12, and is chargedinto a cavity of an unillustrated mold apparatus (see, for example,Patent Document 1).

Patent Document 1 : Japanese Patent Application Laid-Open (kokai) No.2004-50415.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, in the conventional injection apparatus, pellets 19 of resinsupplied via the resin supply port 25 aggregate, as shown in FIG. 2,while being advanced within the groove 24 in a direction indicated by anarrow, whereby a solid bed b, which is composed of a plurality ofpellets 19, is formed within a melt pool r.

In the solid bed b, although heat is easily transferred to pellets 19present on the circumference of the solid bed b, heat is hardlytransferred to pellets 19 located at the interior of the solid bed b.Therefore, a long period of time is required to melt all the pellets 19.Therefore, the heat generated by the heaters h1 to h3 is not efficientlytransferred to all the pellets.

Further, since the solid bed b is formed in such a manner that aplurality of pellets 19 are stacked in the depth direction of the groove24, heat capacity increases. Therefore, even when shearing heat isgenerated in the resin, as shown in FIG. 3, an increase arises in adeveloped distance L1 within which the resin melts completely.

As a result, the length of the screw 14 must be increased accordingly,and, thus, the length of the heating cylinder 11 also must be increased.Therefore, the axial dimension of the injection apparatus increases, anda work of removing and inserting the screw 14 at the time of maintainingthe screw 14 or replacing it with a different one becomes difficult.

Further, since the surface area of the heating cylinder 11 increases,the amount of radiated heat increases, with a resultant decrease inenergy efficiency. In addition, since the resin is uselessly heated,burning of resin; i.e., resin burning occurs. Moreover, although thepellets 19 present at the circumference are melted to a sufficientdegree, the pellets 19 present at the interior are not melted to asufficient degree. In addition, many pellets 19 are melted mainlythrough the generation of shearing heat, as the solid bed b advanceswithin the groove 24. Accordingly, the resin cannot be melted uniformly.Thus, the quality of molded products deteriorates.

An object of the present invention is to solve the above-mentionedproblems in the conventional injection apparatus and to provide aninjection apparatus which can reduce the axial dimension of theinjection apparatus, facilitate the work of removing and inserting ascrew, and improve the quality of molded products.

Means for Solving the Problems

In order to achieve the above object, an injection apparatus of thepresent invention comprises a heating cylinder, a screw which isrotatably disposed within the heating cylinder; and a drive apparatusdisposed at a rear end of the screw.

The screw includes a plasticizing portion which includes a body portionand a flight projectingly formed on an outer circumferential surface ofthe body portion.

An index ε, which is obtained by dividing a value obtained by adding ascrew stroke S and a screw effective length L together by the screwstroke S, satisfies the following relation:

2.0<ε<4.5.

Effects of the Invention

According to the present invention, an injection apparatus comprises aheating cylinder, a screw which is rotatably disposed within the heatingcylinder; and a drive apparatus disposed at a rear end of the screw.

The screw includes a plasticizing portion which includes a body portionand a flight projectingly formed on an outer circumferential surface ofthe body portion.

An index ε, which is obtained by dividing a value obtained by adding ascrew stroke S and a screw effective length L together by the screwstroke S, satisfies the following relation:

2.0<ε<4.5.

In this case, since the index ε satisfies the relation 2.0<ε<4.5, evenwhen the screw is shortened, resin can be melted satisfactorily.Accordingly, the axial dimension of the injection apparatus can bereduced, the work of removing and inserting the screw can be readilyperformed, and the quality of molded products can be improved.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] Cross sectional view showing a main portion of a conventionalinjection apparatus.

[FIG. 2] Schematic view showing a state where resin is melted within theconventional injection apparatus.

[FIG. 3] View used for explaining a developed distance of theconventional injection apparatus.

[FIG. 4] Schematic view showing a main portion of an injection apparatusaccording to a first embodiment of the present invention.

[FIG. 5] Enlarged view showing the main portion of the injectionapparatus according to the first embodiment of the present invention.

[FIG. 6] Schematic view relating to the first embodiment of the presentinvention and showing a state where resin is melted.

[FIG. 7] View used for explaining a developed distance of the injectionapparatus according to the first embodiment of the present invention.

[FIG. 8] Table relating to the first embodiment of the present inventionand for showing an evaluation result as to whether a solid bed wasformed.

[FIG. 9] Schematic view showing a main portion of an injection apparatusaccording to a second embodiment of the present invention.

[FIG. 10] First graph showing melting states of resin.

[FIG. 11] Second graph showing melting states of resin.

[FIG. 12] Table showing a detailed comparison of melting states of resinfor each screw.

[FIG. 13] Table showing a comparison of melting states of resin for eachscrew.

DESCRIPTION OF REFERENCE NUMERALS

-   17: heating cylinder-   20: screw-   31: injection apparatus-   45: flight forming portion-   45 a: body portion-   53: flight

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention will next be described indetail with reference to the drawings. Here, an injection moldingmachine, which is an example molding machine, will be described.

FIG. 4 is a schematic view showing a main portion of an injectionapparatus according to a first embodiment of the present invention. FIG.5 is an enlarged view showing the main portion of the injectionapparatus according to the first embodiment of the present invention.

In these drawings, reference numeral 31 denotes an in-line-screw-typeinjection apparatus. The injection molding machine includes anunillustrated mold apparatus, an unillustrated mold-clamping apparatus,and the injection apparatus 31. The mold apparatus includes a stationarymold (first mold), and a movable mold (second mold). The mold-clampingapparatus includes a stationary platen, to which the stationary mold ismounted, and a movable platen, to which the movable mold is mounted. Themovable platen is advanced and retreated by means of a mold-clampingcylinder, whereby the mold apparatus is closed, clamped, and opened.

The injection apparatus 31 includes a heating cylinder (cylinder member)17; an injection nozzle (nozzle member) 18 attached to the front end ofthe heating cylinder 17; a screw (injection member/metering member) 20disposed within the heating cylinder 17 such that the screw 20 canrotate and can advance and retreat; heaters (heating members) h11 to h13attached to the outer circumference of the heating cylinder so as tosurround the heating cylinder 17; an unillustrated drive apparatusdisposed rearward of the heating cylinder 17; etc.

The screw 20 is composed of a screw body (injection member body) 52 andan injection portion 46 disposed frontward of the screw body 52, and isconnected to the drive apparatus via a shaft portion 51 at the rear end.The screw body 52 includes a flight forming portion (plasticizingportion) 45 and a pressure member (kneading portion) 54 removablyattached to the flight forming portion 45 at its front end. The flightforming portion 45 includes a bar-shaped body portion 45 a and a spiralflight 53 projectingly formed on the outer circumferential surface ofthe body portion 45 a. A spiral groove 67 is formed along the flight 53.In the flight forming portion 45, over the entire region of the flightforming portion 45; i.e., from the front end to the rear end thereof,the flight 53 is formed at a constant pitch, the flight 53 has aconstant outer diameter or a flight crest diameter Di, the body portion45 a has a constant diameter or a flight trough diameter d1, and thegroove 67 has a constant depth.

The pressure member 54 is formed to extend over a predetermined rangeextending frontward from the front end of the flight forming portion 45and to be located adjacent to a reverse-flow prevention apparatus 62.Thus, the pressure member 54 forms a flat region on the surface thereofover a predetermined distance. The pressure member 54 includes aninclined portion (first pressure portion) 71, and a large-diameterportion (cylindrical columnar portion/second pressure portion) 72. Theinclined portion 71 is formed such that its diameter increasesfrontward, and has a conical shape. The large-diameter portion 72 isformed adjacent to the front end of the inclined portion 71 to beintegral therewith. The large-diameter portion 72 has a cylindricalcolumnar shape and has a constant diameter d2 over the entire length.

Further, an unillustrated screw portion is formed at the rear of theinclined portion 71, and an unillustrated screw hole is formed in theflight forming portion 45 such that the screw hole is opened at thefront end surface thereof. Accordingly, the pressure member 54 can beattached to the flight forming portion 45 through screw-engagement ofthe screw portion with the screw hole. Notably, in the presentembodiment, the pressure member 54 is fixed to the flight formingportion 45 by means of screw engagement. However, the pressure member 54can be fixed to the flight forming portion 45 by means of welding inplace of screw engagement.

The diameter of the front end of the inclined portion 71 is made equalto the diameter d2 of the large-diameter portion 72, and the diameter ofthe rear end of the inclined portion 71 is made equal to the flighttrough diameter d1. Notably, in the present embodiment, the outercircumferential surface of the inclined portion 71 has a constantinclination; however, if necessary, the outer circumferential surfacemay be curved in accordance with a predetermined function.

A resin passage (first molding material passage) 73 is formed betweenthe inclined portion 71 and the heating cylinder 17, and a resin passage(second molding material passage) 74 is formed between thelarge-diameter portion 72 and the heating cylinder 17. In this case, asdescribed above, the diameter of the inclined portion 71 increasesfrontward, so that the cross sectional area of the resin passage 73decreases frontward. Since the diameter d2 of the large-diameter portion72 is constant over its length, the cross sectional area of the resinpassage 74 is maintained constant over the entire length of the resinpassage 74.

In the present embodiment, the pressure member 54 includes the inclinedportion 71 and the large-diameter portion 72. However, the pressuremember 54 may be formed by only an inclined portion having noundulations. In this case, the diameter is increased frontward, thediameter of the rear end of the pressure member 54 is made equal to theabove-mentioned flight trough diameter d1, and the diameter of the frontend of the pressure member 54 is made equal to the above-mentioneddiameter d2.

Meanwhile, the injection portion 46 includes a head portion 55 having aconical portion at its front end; a rod portion 56 formed rearward ofand adjacent to the head portion 55; a check ring 57 disposed around therod portion 56; and a seal ring 58 attached to the front end of thescrew body 52. A resin passage (third molding material passage) 75 isformed between the rod portion 56 and the check ring 57.

Further, an unillustrated screw portion is formed at the rear of the rodportion 56, and an unillustrated screw hole is formed in the pressuremember 54 such that the screw hole is opened at the front end surfacethereof. Accordingly, through screw-engagement of the screw portion withthe screw hole, the injection member 46 can be attached to the screwbody 52 with the seal ring 58 pressed against the front end of thepressure member 54. Notably, the head portion 55, the rod portion 56,and the screw portion constitute a screw head (injection member headportion) 61; and the check ring 57 and the seal ring 58 constitute thereverse-flow prevention apparatus 62, which prevents reverse flow ofresin during an injection step.

In a metering step, when the check ring 57 is caused to move forward inrelation to the rod portion 56 as the screw 20 is retreated, the checkring 57 is separated from the seal ring 58, so that the resin passage 75communicates with the resin passage 74, and the reverse-flow preventionapparatus 62 stops its sealing operation. In an injection step, when thecheck ring 57 is caused to move rearward in relation to the rod portion56 as the screw 20 is advanced, the check ring 57 is brought intocontact with the seal ring 58, so that the communication between theresin passage 74 and the resin passage 75 is broken, and thereverse-flow prevention apparatus 62 starts its sealing operation.

The drive apparatus includes a metering motor, serving as a driveportion for metering, and an injection motor, serving as a drive portionfor injection.

A resin supply port (molding material supply port) 65 is formed in theheating cylinder 17 at a predetermined position in the vicinity of therear end thereof. The resin supply port 65 is formed at such a locationthat when the screw is located at the advance limit position within theheating cylinder 17, the resin supply port 65 faces a rear end portionof the groove 67.

A charging section (molding material supply apparatus) 81 for chargingresin is attached to the resin supply port 65, and a hopper (moldingmaterial storage portion) 82 for storing resin is attached to the upperend of the charging section 81. The resin stored in the hopper 82 is fedto the resin supply port 65 via the charging section 81, and is suppliedfrom the resin supply port 65 to the interior of the heating cylinder17.

The charging section 81 includes a cylinder portion 83 extendinghorizontally, a tubular guide portion 84 extending downward from thefront end of the cylinder portion 83, a feed screw 85 rotatably disposedwithin the cylinder portion 83, a feed motor (feed drive portion) 86 forrotating the feed screw 85, a heater (heating member) h21 disposedaround the cylinder portion 83, etc. The cylinder portion 83 isconnected to the hopper 82 at its rear end, and communicates with theguide portion 84 at its front end.

Accordingly, when the feed screw 85 is rotated through drive of the feedmotor 86, the resin within the hopper 82 is supplied into the cylinderportion 83, and caused to advance along a groove formed on the outercircumferential surface of the feed screw 85, so that the resin is fedfrom the front end of the feed screw 85 into the guide portion 84, andfalls within the guide portion 84, whereby the resin is supplied intothe heating cylinder 17. At this time, pellets 19 fall within the guideportion 84 in line, and are supplied into the heating cylinder 17 viathe resin supply port 65.

An annular cooling jacket (cooling apparatus) 88 is formed on theheating cylinder 17 in the vicinity of the resin supply port 65 so as tosurround the heating cylinder 17, the resin supply port 65, and a lowerend portion of the guide portion 84. Water (cooling medium) is suppliedto the cooling jacket 88. This water prevents melting of the resin whichfalls within the guide portion 84 and is supplied into the heatingcylinder 17 via the resin supply port 65.

Notably, S represents a screw stroke, which is a distance between theretreat limit and the advance limit of the screw 20; L represents ascrew effective length, which is a distance between the rear end of theresin supply port 65 and the front end of the screw 20 as measured whenthe screw 20 is located at the advance limit position.

An unillustrated control section is provided so as to control theinjection molding machine; specifically, drive the injection motor, themetering motor, the feed motor 86, etc, and supply electricity to theheaters h11-h13 and h21. The control section includes not only a CPU(computation apparatus), a memory (storage apparatus), but also adisplay section, an operation section, etc. The control section performsvarious computations in accordance with a predetermined program, data,etc. to thereby function as a computer.

In the injection apparatus 31 having the above-described configuration,in a metering step, the feed screw 85 and the screw 20 are rotated intheir normal directions through drive of the feed motor 86 and themetering motor in their normal directions. Thus, the resin supplied fromthe hopper 82 into the cylinder portion 83 is caused to advance alongthe groove of the feed screw 85, and is pre-heated during theadvancement. The resin is then supplied into the guide portion 84 fromthe front end of the cylinder portion 83, and is supplied into theheating cylinder 17 via the resin supply port 65. Notably, within thecylinder portion 83, the resin is preheated to a temperature at whichthe resin does not melt; e.g., a predetermined temperature equal to orless than the glass transition temperature.

The resin supplied into the heating cylinder 17 is caused to advancealong the groove 67, and is heated and melted by the heaters h11 to h13.The pressure of the resin increases gradually as the resin advances tothe front end of the screw body 52 from a pressure increase start pointwhich is shifted rearward from the pressure member 54 by a predetermineddistance.

Subsequently, the resin is caused to pass through the resin passage 73,whereby the pressure of the resin increases further, and is caused toadvance while passing through the resin passage 74. Therefore, the resinis kneaded sufficiently.

At this time, since the check ring 57 is moved forward in relation tothe rod portion 56, communication is established between the resinpassages 74 and 75, so that the resin within the resin passage 74 iscaused to pass through the resin passage 75 to be fed to the spaceforward of the screw head 61. Accordingly, an amount of molten resincorresponding to a single shot is accumulated in the space forward ofthe screw head 61 in a state in which the screw 20 is positioned at theretreat limit position within the heating cylinder 17. Notably, anunillustrated cut is formed in the head portion 55 such that the resinpassage 75 communicates with the space forward of the screw head 61.

Subsequently, in an injection step, the screw 20 is advanced throughdrive of the injection motor, whereby the resin accumulated forward ofthe screw head 61 is injected from the injection nozzle 18, and ischarged into a cavity of the above-described mold apparatus.

Incidentally, as described above, in the screw body 52, the pressuremember 54 is formed in a predetermined range extending from the frontend thereof in such a manner that the pressure member 54 is locatedadjacent to the reverse-flow prevention apparatus 62. Further, thepressure member 54 has a flat outer circumferential surface.

That is, the resin supplied from the resin supply port 65 is caused toadvance within the groove 67, while being guided by the flight 53, asthe screw 20 rotates in a metering step. However, when the resin reachesthe pressure member 54, the resin is not guided by the flight, becausethe flight is not formed on the pressure member 54, so that the force bywhich the resin is advanced decreases.

Accordingly, the moving speed of the resin decreases in the resinpassages 73 and 74. Therefore, the pressure member 54 functions as amovement restriction member for restricting advancement of the resincaused to advance within the groove from the rear. As a result, sinceadvancement of the resin within the groove 67 is restricted, in a regionforward of the pressure increase start point, the resin pressureincreases toward the front.

Further, in the pressure member 54, the diameter of the inclined portion71 increases toward the front so that the cross sectional area of theresin passage 73 decreases toward the front, and the diameter d2 of thelarge-diameter portion 72 is greater than the flight trough diameter d1but smaller than the flight crest diameter Di.

Accordingly, the function of the pressure member 54 as a movementrestriction member can be enhanced further, whereby the pressure ofresin in the region located forward of the pressure increase start pointcan be increased further. Notably, the radial distance t1 between theouter circumferential surface of the body portion 45 a and the outercircumferential edge of the flight 53 is represented by the followingequation.

t1=(Di−d1)/2

Further, when the distance between the outer circumferential surface ofthe large-diameter portion 72 and the circumferential edge of the flight53 is represented by t2, the ratio of the distance t2 to the distancet1; i.e., the ratio t2/t1, becomes smaller than 1.

As a result, in a state in which the screw 20 is located at the advancelimit position, a region extending from a molding material supply point,which is formed at a position corresponding to the rear end of the resinsupply port 65, to the pressure increase start point constitutes asupply portion; a region extending from the pressure increase startpoint to the front end of the flight forming portion 45 constitutes acompression portion; and a region extending from the front end of theflight forming portion 45 to the front end of the pressure member 54constitutes a kneading (metering) portion. Therefore, plasticizationsimilar to that performed in conventional injection apparatuses can beperformed, so that resin can be kneaded sufficiently. Further, since thepressure of the resin after being melted can be increased at thekneading portion, kneading of resin can be performed more sufficiently.

Further, the resin pressure at the compression portion can be increasedthrough mere formation of the large-diameter portion 72, and the flighttrough diameter d1 is not required to be changed along the axialdirection of the flight forming portion 45.

Since the shape of the screw 20 can be simplified, the cost of the screw20 can be lowered. Further, the simplified shape decreases the number oflocations where resin stagnates, to thereby prevent occurrence of resinburning, whereby the quality of molded products can be improved.

Incidentally, if pellets of the resin supplied via the resin supply port65 aggregate while being caused to advance within the heating cylinder17, with the result that a solid bed b composed of a plurality of resinpellets 19 (see FIG. 2) is formed, a long period of time is required tocompletely melt the pellets 19.

In order to solve this problem, in the present embodiment, agroove-depth setting region for preventing formation of the solid bed bis defined in a predetermined section of the flight forming portion 45with respect to the length direction thereof. In the groove-depthsetting region, the ratio γ1 of a groove depth τ1 to a diameter δ1 ofpellets 19 (γ1=τ1/δ1) is set to fall within the following range:

1≦γ1≦2.5,

and preferably,

1≦γ1≦2.0.

Notably, since the groove depth τ1 is equal to the distance t1, thefollowing equation stands:

τ1=(Di−d1)/2.

In the present embodiment, the pellets 19 have a spherical shape.However, in the case where the pellets 19 have a non-spherical shape,the diameter δ1 of the pellets 19 may be the largest one of diameters ofvarious portions of each pellet 19; i.e., the maximum diameter, thesmallest one of diameters of various portions of each pellet 19; i.e.,the minimum diameter, or an intermediate value (e.g., mean value)between the maximum diameter and the minimum diameter.

The groove-depth setting region is formed over such an axial length thatformation of the solid bed b can be prevented, and preferably formedover a section extending from a point which corresponds to the rear endof the resin supply port 65 when the screw 20 is located at the advancelimit position to the forward end of the flight forming portion 45.Further, the groove-depth setting region may be formed over a sectionextending from the point corresponding to the rear end of the resinsupply port 65 to a location where the resin melts completely, or may beformed to extend forward from the point corresponding to the rear end ofthe resin supply port 65 over a distance equal to the length of thescrew stroke S.

Notably, in actuality, the groove-depth setting region is set by theaxial length of the screw 20 or the length of the groove 67.

Next, a state where resin melts will be described.

FIG. 6 is a schematic view relating to the first embodiment of thepresent invention and showing a state where resin is melted. FIG. 7 is aview used for explaining a developed distance of the injection apparatusaccording to the first embodiment of the present invention.

In these drawings, reference numeral 17 denotes a heating cylinder, 20denotes a screw, 53 denotes a flight, 67 denotes a groove, 19 denotespellets, and r represents a melt pool formed by molten resin.

As described above, the ratio γ1 is set to fall within the followingrange:

1≦γ1≦2.5,

and preferably,

1≦γ1≦2.0.

Therefore, in the groove 67, two pellets 19 cannot be stacked in thedepth direction of the groove 67 (radial direction). Accordingly, thepellets 19 do not aggregate and are caused to advance along the groove67 in a direction of a solid line allow, while being arranged laterally.Further, in the above-described injection apparatus 31 (FIG. 4), thefriction coefficient of the inner circumferential surface of the heatingcylinder 17 is set to be larger than that of the outer circumferentialsurface of the screw 20 so that molten resin advances when the screw 20is rotated. Accordingly, as the screw 20 rotates, the pellets 19 advancewithin the groove 67, while rolling (rotating) due to friction with theinner circumferential surface of the heating cylinder 17.

As a result, the solid bed b (see FIG. 2) is not formed by the pellets19, and the pellets 19 are heated in a state where their heat capacityis small. Accordingly, the resin can be melted within a short period oftime, and, as shown in FIG. 7, a developed distance L2 within which theresin melts completely can be shortened. Thus, the screw 20 can beshortened accordingly.

Further, since the heating cylinder 17 can also be shortened, the axialdimension of the injection apparatus 31 decreases, and a work ofremoving and inserting the screw 20 can be readily performed when thescrew 20 is maintained or replaced with a different one.

Since the surface area of the heating cylinder 17 decreases, the amountof radiated heat decreases, so that the energy efficiency of theinjection apparatus can be increased. In addition, since the resin isnot uselessly heated, occurrence of resin burning can be suppressed.

Moreover, the space formed between the inner circumferential surface ofthe heating cylinder 17 and the screw 20 functions as a heat supplyspace for supplying heat from the heaters h11 to h13 to the pellets 19.Since the pellets 19 advance within the groove 67, while rolling incontact with the inner circumferential surface of the heating cylinder17, as indicated by broken-line arrows, the heat of the heaters h11 toh13 is transferred to the pellets 19 via the heating cylinder 17 bymeans of rolling heat transfer. Accordingly, the resin can be heated andmelted efficiently and uniformly. As a result, the quality of moldedproducts can be improved.

Notably, since the pellets 19 are pre-heated within the cylinder portion83, melting is started immediately when the pellets 19 are supplied intothe heating cylinder 17. Accordingly, the time required to completelymelt the pellets 19 can be shortened, whereby the screw 20 can beshortened further, and the axial dimension of the injection apparatus 31can be reduced further.

In addition, since the pellets 19 are smoothly advanced within thegroove 67, shearing heat generation can be suppressed. Accordingly,resin burning does not occur, and the quality of molded products can beimproved.

Incidentally, if a large amount of resin is supplied into the heatingcylinder 17 via the resin supply port 65 within a short period of timewithout the supply amount being controlled, the above-described heatsupply space is filled with an excess amount of resin, and a pressure isapplied to pellets 19 before being melted within the groove 67, so thatthe pellets 19 restrain their movements one another. Consequently, thepellets 19 do not roll, and the heat of the heaters h11 to h13 is nottransferred to the pellets 19 by means of rolling heat transfer. In sucha case, a portion of the pellets 19 do not melt, so that it becomesimpossible to uniformly melt the resin. In addition, a jamming failureof the screw 20 occurs.

In order to solve the above-described drawback, supply-amount controlprocessing means (supply-amount control processing section) of the CPUperforms supply-amount control processing so as to control the amount ofthe resin supplied into the heating cylinder 17 by controlling therotational speed of the feed motor 86. In such a case, a rotationalspeed to which the feed motor 86 is controlled; i.e., a targetrotational speed, is set so that, as shown in FIG. 4, a predeterminedamount of pellets 19 are caused to continuously fall and are supplied tothe resin supply port 65.

As described above, in the present embodiment, since the supply amountof the resin is controlled, the heat supply space is appropriatelyfilled with the resin, and no pressure is applied to pellets 19 beforebeing melted within the groove 67. Therefore, the pellets 19 do notrestrain their movements one another, and are caused to roll and move.Consequently, the heat of the heaters h11 to h13 is transferred to thepellets 19 by means of rolling heat transfer, so that it becomespossible to uniformly melt the resin, and to prevent occurrence of ajamming failure of the screw 20. As a result, the quality of moldedproducts can be improved. In addition, since the resin can be meltedsufficiently, the developed distance L2 can be shortened reliably, andthe screw 20 can be shortened sufficiently.

Moreover, heating-amount adjustment processing means (heating-amountadjustment processing section) of the CPU performs heating-amountadjustment processing so as to adjust the amount of heating of the resinby controlling the supply of electricity to the heaters h11 to h13, tothereby control the temperature of the resin. Accordingly, the speed atwhich the pellets 19 roll; i.e., rolling speed, can be controlled,whereby the developed distance L2 can be controlled.

FIG. 8 is a table relating to the first embodiment of the presentinvention and for showing an evaluation result as to whether the solidbed was formed.

In FIG. 8, X represents that the solid bed b was formed, and οrepresents that the solid bed b was not formed.

As shown in FIG. 8, the solid bed b was not formed if the ratio γ1 was1.0, 2.0, and 2.5, and the solid bed was formed if the ratio was 3.0 and3.5.

As described above, in the present embodiment, the ratio γ1 of thegroove depth τ1 to the diameter δ1 is set to fall within the followingrange:

1≦γ1≦2.5,

and preferably,

1≦γ1≦2.0.

In addition, the charging section 81 is provided in order to preheat thepellets 19, and the amount of resin supplied to the heating cylinder 17is controlled. Thus, the conditions for melting resin; i.e., the meldingconditions, are satisfied. However, if the design conditions of thescrew 20 such as the screw stroke S and the screw effective length L arenot appropriate, resin cannot be melted properly. That is, when thescrew effective length L is less than a proper value set in accordancewith the screw stroke S, resin cannot be melted completely. When thescrew effective length L is greater than the proper value, a time overwhich resin advances within the heating cylinder 17 is excessively long,so that resin burning occurs.

In view of the above, in the present embodiment, an index ε, whichrepresents the degree of properness of the design conditions of thescrew 20, is obtained by the following equation; i.e., by dividing, bythe screw stroke S, a value obtained by adding the screw stroke S andthe screw effective length L together.

ε=(S+L)/S

The index ε was changed to assume different values, and the meltingstate of resin was observed for each value of the index ε.

As a result, it was found that when the index ε is set to fall withinthe following range:

2.5<ε<4.5,

resin can be melted satisfactorily. That is, resin was able to be meltedto a sufficient degree, and occurrence of resin burning was able to beprevented.

Notably, when the index ε is set to fall within the following range:

3.0<ε<4.0,

resin was able to be melted more satisfactorily. That is, resin was ableto be melted completely, and occurrence of resin burning was able to beprevented without fail.

Notably, in the injection apparatus 31, in view of the resin meltingstate, the screw effective length L can be approximated to a heatingcylinder length Lh; i.e., the distance between the rear end of theheating cylinder 17 and the front end of the injection nozzle 18.

In this case, an index ε′, which represents the degree of properness ofthe design conditions of the screw 20, is obtained by the followingequation; i.e., by dividing, by the screw stroke S, a value obtained byadding the screw stroke S and the heating cylinder length Lh together.

ε′=(S+Lh)/S

The index ε′ was changed to assume different values, and the meltingstate of resin was observed for each value of the index ε′.

As a result, it was found that when the index ε′ is set to fall withinthe same range as that for the index ε, resin can be meltedsatisfactorily.

Incidentally, in the injection apparatus 31 having the above-describedconfiguration, the flight 53 formed on the screw 20 has a single-flightstructure; i.e., is composed of a single projection which iscontinuously formed to spirally extend. Accordingly, the lead of theflight 53 (pitch of the flight 53); i.e., an axial distance over which apoint on the flight 53 advances when the point moves along the flight 53over a distance corresponding one turn of the flight 53, is made equalto the width of the groove 67 as measured along the axial direction ofthe screw 20.

Accordingly, the resin, which is supplied to the heating cylinder 17 viathe resin supply port 65 after having fallen within the guide portion84, is caused by the flight 53 to advance within the single groove 67continuously formed to spirally extend. At that time, if the width ofthe groove 67 is greater than the diameter δ1 of the pellets 19, a largenumber of the pellets 19 are accommodated within the groove 67, and apressure acts on each of the pellets 19, so that each of the pellets 19restricts movements of other pellets 19. As a result, it becomesimpossible to melt resin to a sufficient degree.

In contrast, in the case where the lead is shortened, and the width ofthe groove 67 is decreased, the groove 67 becomes longer accordingly, sothat the time over which resin resides within the heating cylinder 17increases, and resin burning may occur.

In view of the above-described problem, an injection apparatus accordingto a second embodiment of the present invention can prevent the pellets19 from mutually restricting their movements, can melt resin to asufficient degree, and does not cause resin burning. The injectionapparatus according to the second embodiment will be described. Notably,components having the same structures as those in the first embodimentare denoted by the same reference numerals, and their repeateddescriptions are omitted. For the effect that the second embodimentyields through employment of the same structure, the description of theeffect of the first embodiment is incorporated herein by reference.

FIG. 9 is a schematic view showing a main portion of the injectionapparatus according to the second embodiment of the present invention.

In FIG. 9, reference numeral 45 denotes a flight forming portion 45serving as a plasticizing portion. The flight forming portion 45includes a bar-shaped body portion 45 a and a spiral flight 53projectingly formed on the outer circumferential surface of the bodyportion 45 a. A spiral groove 67 including first and second grooves 67 aand 67 b is formed along the flight 53. In the present embodiment, theflight 53 has a double-flight structure; i.e., includes first and secondflight portions 53 a and 53 b, which are continuously formed to spirallyextend. The first and second grooves 67 a and 67 b are formed along thefirst and second flight portions 53 a and 53 b, respectively.Accordingly, the resin, which is supplied to the heating cylinder 17 viathe resin supply port 65 (the molding material supply port) after havingfallen within the guide portion 84, is divided into two portions whichare caused by the first and second flight portions 53 a and 53 b toindividually advance within the first and second grooves 67 a and 67 b.

In this case, even when the leads of the first and second flightportions 53 a and 53 b are made equal to that of the flight 53 of thefirst embodiment, the widths of the first and second grooves 67 a and 67b can be made half the width of the groove 67 of the first embodiment,whereby the amount of the pellets 19 (FIG. 7) accommodated in each ofthe first and second grooves 67 a and 67 b can be halved. Accordingly,within the first and second grooves 67 a and 67 b, pressure does not acton the pellets 19, and the pellets 19 can be prevented from mutuallyrestricting their movements. As a result, resin can be melted to asufficient degree.

Further, since the lead of the first and second flight portions 53 a and53 b does not increase, the time over which resin resides within theheating cylinder 17 does not increase, and resin burning does not occur.

In the present embodiment, while the index ε was changed to assumedifferent values, the melting state of resin was observed for each valueof the index ε.

As a result, as shown in FIGS. 10 to 13 which are described later, itwas found that when the index ε is set to fall within the followingrange:

2.0<ε<4.0,

resin can be melted satisfactorily. That is, resin was able to be meltedto a sufficient degree, and occurrence of resin burning was able to beprevented.

Notably, when the index ε is set to fall within the following range:

2.5<ε<3.5,

resin was able to be melted more satisfactorily. That is, resin was ableto be melted completely, and occurrence of resin burning was able to beprevented without fail.

Next, there will be described the results of comparison between themelting state of resin when the conventional injection apparatus wasused, and the melting state of resin when the injection apparatus 31 ofthe first or second embodiment was used.

FIG. 10 is a first graph showing melting states of resin. FIG. 11 is asecond graph showing melting states of resin. FIG. 12 is a table showinga detailed comparison of melting states of resin for each screw. FIG. 13is a table showing a comparison of melting states of resin for eachscrew. In FIG. 10, the horizontal axis represents the index ε, and thevertical axis represents the temperature of resin when it reaches thefront end of the flight forming portion 45 (FIG. 9). In FIG. 11, thehorizontal axis represents the index ε, and the vertical axis representsthe time over which resin resides within the heating cylinder 17 afterhaving melted completely. In FIG. 12, the horizontal axis represents thescrew stroke S, and the vertical axis represents the screw effectivelength L.

In these drawings, Q1 shows the melting state of resin in the case wherea standard screw of a conventional injection apparatus is used; Q2 showsthe melting state of resin in the case where the injection apparatus 31(FIG. 4) of the present invention is used and the screw 20, serving asan injection member and an metering member, is of the single flighttype; and Q3 shows the melting state of resin in the case where theinjection apparatus 31 of the present invention is used and the screw 20(FIG. 9) is of the double flight type in the second embodiment of thepresent invention. Further, Q4 shows the time over which resin resideswithin the heating cylinder 17 after having melted completely in thecase where the injection apparatus 31 of the present invention is usedand the screw 20 is of the single flight type; and Q5 shows the timeover which resin resides within the heating cylinder 17 after havingmelted completely in the case where the injection apparatus 31 of thepresent invention is used and the screw 20 is of the double flight type.Ta represents the temperature at which resin melts completely.

As described above, in the case where the screw 20 is of the doubleflight type, pressure does not act on the pellets 19 within the firstand second grooves 67 a and 67 b, and the pellets 19 can be preventedfrom mutually restricting their movements as compared with the screw 20of the single flight type. As a result, resin can be melted to asufficient degree, whereby the temperature represented by the state Q3can be set higher than that represented by the state Q2.

In FIGS. 12 and 13, X represents the case where resin was not able to bemelted sufficiently, or occurrence of resin burning was not able to beprevented; A represents the case where resin was able to be melted to asufficient degree, and occurrence of resin burning was able to beprevented; and ο represents the case where resin was able to be meltedmore sufficiently (i.e., resin was able to be melted completely) andoccurrence of resin burning was able to be prevented without fail.

FIG. 12 also shows as evaluation result of the states of resin that wasplasticized and melted using the screws 20 of the single flight type andthe double flight type each having the flight crest diameter Di (FIG. 5)of 22[Φ: mm], 32[Φ: mm], 63[Φ: mm], and 84[Φ: mm], and the screw strokeS and the screw effective length L, which were determined in accordancewith the flight crest diameter Di.

In addition, in FIG. 12, on the left side of the vertical linerepresenting each flight crest diameter Di, the evaluation result isshown when the screw 20 of the single flight type was used; and on theright side of the vertical line, the evaluation result is shown when thescrew 20 of the double flight type was used.

Further, lines Q11 to Q14 represent the cases when the index ε was 2.0,2.5, 4.0, and 4.5, respectively. As described below, it is found that,when the screw is of the single flight type, the melting states of resinchange at the boundaries of the lines Q12 and Q14, and when the screw isof the double flight type, the melting states of resin change at theboundaries of the lines Q11 and Q13.

That is, as shown in FIGS. 12 and 13, in the case where the screw 20 isof the single flight type, when the index ε is set to fall within thefollowing range:

2.5<ε<4.5,

resin was able to be melted to a sufficient degree, and occurrence ofresin burning was able to be prevented. When the index ε is set to fallwithin the following range:

3.0<ε<4.0,

resin was able to be melted completely, and occurrence of resin burningwas able to be prevented without fail.

In the case where the screw 20 is of the double flight type, when theindex ε is set to fall within the following range:

2.0<ε<4.0,

resin was able to be melted to a sufficient degree, and occurrence ofresin burning was able to be prevented. When the index ε is set to fallwithin the following range:

2.5<ε<3.5,

resin was able to be melted completely, and occurrence of resin burningwas able to be prevented without fail.

In the case where the screw 20 is of the single flight type, in theregion where the index ε is equal to or less than 2.5, the developeddistance for melting resin cannot be secured sufficiently, because thescrew effective length L is short as compared with the screw stroke S.Accordingly, resin cannot be melted sufficiently, and molding failureoccurs.

In the region where the index ε is equal to or greater than 4.5 in thecase where the screw 20 is of the single flight type, and in the regionwhere the index ε is equal to or greater that 4.0 in the case where thescrew 20 is of the double flight type, the screw effective length Lbecomes excessively long as compared with the screw stroke S, so thatthe time over which resin resides within the heating cylinder 17increases, and resin burning may occur.

In the region where the index ε is equal to or less than 2.0, since thescrew effective length L becomes short as compared with the screw strokeS, the screw head 61 is positioned rearward of the resin supply port 25when the screw is located at the retreat limit position. Accordingly,injection cannot be performed in the injection apparatus 31.

In the above embodiments, the pellets 19 are caused to fall within theguide portion 84 while forming a single line and are supplied to theresin supply port 65. However, the pellets 19 are not necessarilyrequired to be supplied to form a single line, so long as clearances areproduced between the pellets 19 between the heating cylinder 17 and thescrew 20 so as to prevent application of pressure to the pellets 19before being melted. For example, application of pressure to the pellets19 can be prevented by supplying a preset amount of resin at a timeevery time a preset time elapses.

The present invention is not limited to the above-described embodiments.Numerous modifications and variations of the present invention arepossible in light of the spirit of the present invention, and they arenot excluded from the scope of the present invention.

1-3. (canceled)
 4. An injection apparatus comprising: (a) a heatingcylinder; (b) a screw rotatably disposed within the heating cylinder andincluding a flight on an outer circumferential surface thereof; and (c)a drive apparatus disposed at a rear end of the screw, wherein (d) thescrew includes a plasticizing portion which includes a body portion andthe flight projectingly formed on an outer circumferential surface ofthe body portion; and wherein (e) an index ε, which is obtained bydividing a value obtained by adding a screw stroke S of the screw and ascrew effective length L of the screw together by the screw stroke S,satisfies the following relation:2.0<ε<4.5.
 5. An injection apparatus according to claim 4, wherein thescrew includes a section in which a ratio γ1 of a groove depth τ1, whichis the depth of a groove formed along the flight, to a diameter δ1 of amolding material falls within the following range:1≦γ1≦2.5.
 6. An injection apparatus according to claim 4, wherein anindex ε′, which is obtained by dividing a value obtained by adding thescrew stroke S and a heating cylinder length Lh of the heating cylindertogether by the screw stroke S, satisfies the following relation:2.0<ε<4.5.
 7. An injection apparatus according to claim 4, comprising amolding material supply apparatus which supplies a molding material intothe heating cylinder in a manner that the molding material does notstack on one another in the heating cylinder.
 8. An injection apparatusaccording to claim 4, (a) the screw includes the plasticizing portion onwhich the flight is formed and configured to plasticize the moldingmaterial, and a pressure member disposed at the front end of theplasticizing portion and including an outer diameter equal to or greaterthan an outer diameter of the plasticizing portion; and wherein (b) aflight is not formed on the pressure member.
 9. An injection apparatusaccording to claim 4, wherein multiple flights are formed on theplasticizing portion.
 10. An injection method of an injection apparatuscomprising: a heating cylinder; a screw rotatably disposed within theheating cylinder and including a flight on an outer circumferentialsurface thereof; and a drive apparatus disposed at a rear end of thescrew, the screw including a plasticizing portion which includes a bodyportion and the flight projectingly formed on an outer circumferentialsurface of the body portion; and an index ε, which is obtained bydividing a value obtained by adding a screw stroke S of the screw and ascrew effective length L of the screw together by the screw stroke S,satisfying the following relation:2.0<ε<4.5, wherein a molding material is supplied into the heatingcylinder in a manner that the molding material does not stack on oneanother in the heating cylinder.
 11. An injection method according toclaim 10, wherein (a) the molding material is plasticized in theplasticizing portion; and (b) the molding material is kneaded by apressure member disposed at a front end of the plasticizing portion.